Effect on growth, sugar consumption, and aerobic ethanol fermentation of homologous expression of the sugar transporter gene Pshxt1 in the white rot fungus Phanerochaete sordida YK-624

Abstract

Major facilitator superfamily (MFS) transporters are found in all organisms. Although numerous studies have examined the functions of yeast and mold MFS transporters in terms of sugar affinity and metabolic regulation, no functional analyses of MFS sugar transporters in white rot fungi have been reported. This study identified an MFS sugar transporter gene (Pshxt1) of the white rot fungus Phanerochaete sordida YK-624 expressed in liquid culture containing low concentrations of nitrogen source. Homologous expression of Pshxt1 dramatically increased the rates of glucose, fructose, mannose, and xylose consumption. Galactose consumption increased slightly but significantly. These data suggest that Pshxt1 has broad affinity for monosaccharides. In contrast, a transformant homologously expressing Pshxt1 consumed glucose in preference to xylose in wood enzymatic-digestion liquor and liquid culture. Additionally, homologous expression of Pshxt1 improved mycelial growth, aerobic ethanol production, and simultaneous aerobic saccharification and fermentation efficiency, whereas secretion of the ligninolytic enzyme manganese peroxidase was clearly decreased in the presence of glucose by Pshxt1 expression. These results suggest that Pshxt1 is involved in the repression of ligninolytic enzyme activity via carbon catabolite repression at sufficiently high glucose concentrations for activation of primary metabolism.